First, the network of linked computers is rapidly gaining users. Second, the kind of data traffic transiting the network is becoming alarmingly bulky. Unless companies offering Internet service respond, several experts warn, parts of the Internet will get as clogged and cumbersome as rush-hour traffic in Los Angeles.

''There's a lot of congestion around the system and I think it's only going to get worse,'' says Hal Varian, an economics professor at the University of Michigan in Ann Arbor. ''People ... have expectations for the Internet that it's not going to be able to keep up with,'' adds Roger Bohn, a management professor at the University of California at San Diego.

The main culprit is a slew of multimedia technologies including the large graphics files used on the Internet's World Wide Web and the digital video and audio messages exchanged on the Internet. These files are far larger than the text-based traffic for which the Internet was designed. ''The network is generally more fragile than many people think,'' says Hans-Werner Braun of the San Diego Supercomputer Center.

Already, the Internet has experienced incidents of congestion. In February, for instance, a Swedish researcher inadvertently flooded the Multicast Bone -- Internet's video and audio carrier -- by broadcasting video of an empty room. For two days, video conferences in the Netherlands, California, and Colorado were disrupted.

Eventually, some experts argue, Internet-service companies will bring so much capacity on-line that congestion problems will disappear. ''It may be that technology will bail us out,'' Professor Varian says. But ''between now and [then] ... there are going to be times when supply and demand are not going to be in sync.''

Pricing is the crucial issue. If it costs as much to send an 800-byte electronic-mail message as it does to send 1 million bytes of digital video, then users have no incentive to limit their multimedia use. Mr. Braun envisions college students flooding the Internet with video calls to their boyfriends and girlfriends.

Some video technologies have methods of limiting on-line resource use, but the Internet lacks a comprehensive accounting method.

Instead, many Internet-service providers are turning to flat-rate billing. ''When you're ... surfing the Net, you don't want to have a meter running,'' says Jim Bergmann, a spokesman for Performance Systems International. The Herndon, Va., company is rolling out PipelineUSA where, for a monthly fee users get 29 hours of access with each extra hour costing $1.50. Such time-based charges do make multimedia a little more expensive, because video and audio takes longer to transmit. But some argue there are better accounting methods.

Braun, for example, suggests a tiered system where users pay a first-class premium if they want their data to go through quickly, while others can send files free but with no guarantee when or if they will arrive. Varian at the University of Michigan proposes setting up electronic toll booths at Internet congestion points that start charging users when traffic gets too heavy.

Van Jacobson staff scientist at Lawrence Berkeley national laboratory in Berkeley, Calif., says, these pricing issues represent a battle for the future of the Internet. ''You have to be very careful in [choosing] the billing and accounting system that does good and not harm.'' Since the Internet was built by people who could publish information there at little or no cost, charging these ''senders'' of information will destroy the system's diversity, he argues. And if advertisers step in to pay the senders' bill, ''you're basically going to get TV, and we can do better than that.''

His solution: charge the information receivers. He believes they'll pay to download the popular multimedia on the Internet.